1. Field of the Invention
This invention generally relates to annunciator apparatus and more particularly to apparatus that announces the unauthorized or inadvertent removal of a plug from an electrical receptacle.
2. Description of Related Art
The removal of an electrical plug from a receptacle is a common occurrence. In many situations this step occurs as a normal event. However, in others this step represents an unauthorized or inadvertent action that requires some immediate response. For example, removing the plug of an electrical appliance in a store may indicate that someone is stealing the appliance. In other situations the removal of the plug may indicate that critical apparatus has ceased to function. In these or other situations it is important to announce the occurrence of such a step by audible or electrical signalling.
These situations, particularly attempted thefts of electrical equipment, have led to the development of various theft deterring apparatus. The simplest apparatus for deterring theft comprises mechanical locking assemblies, such as cables and locks, that physically bind an appliance to a wall, counter or other fixture to prevent its physical removal. Such mechanical assemblies, however, can be cumbersome to use, especially in stores where individuals properly may move the appliances. It is relatively easy for an individual intent on stealing the appliance to defeat these mechanical locking assemblies and remove the appliance. Moreover, these assemblies do not inherently have any capability to announce the occurrence of unauthorized actions.
There is a range of alarms and other annunciator apparatus that provides on-site or remote signalling that are used in a theft deterring role. In one approach electrical receptacles are modified to provide mechanical or optical switching functions that respond to the presence or absence of a ground or neutral plug terminal or the like. Alarm circuits provide an alarm whenever a plug is not present. The following U.S. Pat. Nos. disclose various embodiments of such apparatus:
______________________________________ 3,090,948 (1963) Cremer 3,192,518 (1965) Sliman 4,097,843 (1978) Basile 4,591,732 (1986) Neuenschwander 4,845,719 (1989) Posey ______________________________________
In accordance with other approaches separate electronic monitoring units mount on appliances or centrally disposed electronic circuits monitor wire lengths or other conditions that could indicate the removal of an electrical plug. The following U.S. Pat. Nos. disclose apparatus of this general category:
______________________________________ 4,327,360 (1982) Brown 4,680,574 (1987) Ruffner 4,736,195 (1988) McMurtry et al 4,945,335 (1990) Kimura et al ______________________________________
The following U.S. Pat. Nos. disclose apparatus that monitors the insertion or removal of a plug from a receptacle:
______________________________________ 4,075,617 (1978) Wireman Canada 547,706 (1957) Barnes 4,028,691 (1977) Zeder 4,658,242 (1987) Zeder 4,935,725 (1990) Turan ______________________________________
The Wireman patent discloses a structure including modified poles in an electrical receptacle. Specifically each receptacle contains an added spring coil between a neutral connection and an auxiliary contact. The auxiliary contact has insulating portions on either side of a conductive portion. Each insulating portion isolates the neutral and auxiliary connections when a plug is either in place or removed. A momentary contact occurs as a plug is inserted or removed. Alarm circuitry associated with the receptacle responds to both transient conditions by sounding an alarm. An operator must shift the system to a test mode to disable the alarm circuit before inserting a plug. If the system is not in a test mode, plug insertion will produce an alarm. Thus, this apparatus may produce false indications of problems unless specific operating steps are followed.
The Barnes patent discloses a current responsive signalling device. The insertion of a plug into the device brings a contact bar into circuit with a pair of contact arms. If the plug is removed, the circuit through the contact bar and contact arms is broken. If multiple plug positions are included in a receptacle, plugs or alternative devices apparently must be inserted in both receptacle positions to silence any alarm. Otherwise the connection between different contact arms apparently would be broken by an empty receptacle position. This condition interrupts current through a relay causing a switch to close and sound the alarm.
In accordance with the Zeder U.S. Pat. No. 4,028,697, filed by the same Applicant as the present invention, a plunger extends through the center of each receptacle of a duplex outlet. Each plunger controls corresponding external switching contacts that constitute an input to an alarm circuit. Any time a plug is removed, spring bias on the corresponding switch contacts opens the switch and an alarm sounds. A special cover can be located in any unused pole position to prevent erroneous alarms, but such covers are subject to being lost. The plunger can be broken; when this occurs, the entire receptacle must be replaced. It is also possible to block the plunger while the plug is installed and then remove the plug without any alarm. Despite these characteristics, apparatus constructed in accordance with the Zeder patent has been accepted for a number of applications where theft deterrence and other monitoring are important.
In accordance with the Zeder U.S. Pat. No. 4,658,242, filed by the same Applicant as the present invention, an alarm circuit relies upon a low impedance through an appliance to disable or inhibit an alarm. More specifically, so long as a low impedance exist between certain terminals, voltages established in the circuit prevent a detector circuit and latch from sounding an alarm. When the impedance between these terminals increases, as by removal of the appliance or by turning off the appliance, the signals shift and enable the alarm to sound. If no appliance is present the alarm sounds. Consequently a low impedance device, such as a jumper, must be connected in the detection circuit to prevent false alarms. If multiple positions are available for receiving components, then if any position is empty, the alarm sounds.
The Turan patent discloses a security system for merchandise and electrical appliances and telephones. The security system includes an electrical receptacle having a plurality of output locations. A modular socket removably engages with outlet locations in the receptacle. When engaged, electrical contacts in the socket are connected to corresponding electrical contacts in the receptacle. The socket is adapted to receive a plug in an electrical and mechanical engagement. If the plug is removed from the socket or a cable connected to the plug is cut, an alarm sounds. However, removal of the socket from the receptacle does not apparently produce an alarm. Moreover, if an installed socket is empty an alarm will sound.